What NZ sea lion whiskers tell us about by-catch
Friday, 22 February 2019
New research on the whiskers of sea lions confirms that the endangered species is at risk from changing environmental conditions, including climate change.
The research also points out yet again that the fishing industry remains a significant threat to NZ sea lions.
Dr Louise Chilvers of the the School of Veterinary Science at Massey University, collected whiskers from 35 adult female sea lions on the Auckland Islands and used stable isotope analysis to uncover their lifelong diet.
The results showed that these female sea lions fall into two groups. Thirteen fed near the bottom and 18 fed in the water column. Just four animals provided 'slight' evidence of feeding in both locations and were mostly water column or mesopelagic feeders.
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'This research confirms that female NZ sea lions at the Auckland Islands are showing long-term individual fidelity to diet, foraging location and strategy,' wrote Chilvers in the journal Endangered Species Research earlier this month.
'Therefore, this population is likely to be highly susceptible to environmental change and anthropogenic impacts, as they cannot or do not have the ability to alter foraging strategies when conditions change.'
It's predicted that climate change will warm the world's oceans, including around the Auckland Islands, about 500 kilometres south of Bluff.
The whisker research also confirmed that the females feeding in the water column were using the same territory as the fishing industry and more likely to be captured or entangled by fisheries gear.
The industry continues to kill sea lions around the Auckland Islands. Five confirmed deaths have been observed so far this fishing season, including four by seafood company Sanford. It pulled two vessels out of the area earlier this month, at least temporarily.
The industry killed two sea lions in 2018. These animals were landed, dead, on the fishing boat deck, Chilvers said. Another 18 were estimated to have died. Three sea lions were killed in 2017. Another 15 were estimated to have died.
The industry uses 'exclusion devices' designed to release sea lions if they are caught in fishing gear. While those devices work to some extent, they also 'obscure' subsequent deaths and failed reproduction, according to a 2017 study by Stefan Meyer and Bruce Robertson of Otago University and Chilvers. That study has been challenged by other academics.
The Department of Conservation estimates there are about 12,000 NZ sea lions, most in breeding colonies on the Auckland and Campbell subantarctic islands.
In recent years, breeding locations have been observed in Stewart Island, Otago and Southland. Before human arrival, the animals, Phocarctos hookeri, bred from Cape Reinga in the Far North all the way down to the subantarctic islands.
Historically, sea lions thrived in warmer waters and eating a somewhat different diet. It was a worry that the largest remaining population, on the Aucklands, showed low adaptability.
DOC released it's annual subantarctic population survey last week. 'The results show that overall the population remains reasonably stable, but concerns remain about high pup mortality,' said DOC's manager of marine species and threats, Ian Angus.
'The data shows that the species is not out of danger yet and that it's important we work hard to ensure that all threats to these beautiful creatures are reduced in some way,' he said.
Using whiskers was 'faster, less invasive and more cost-effective method' of observing diet than other methods, Chilvers reported.